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HER2-positive breast cancer (and HER2-low)

Hearing that your cancer is HER2-positive can sound scary, but it's one of the biggest success stories in breast cancer: drugs made for HER2 have changed the outlook for many people.

ℹ️ General information to help you and your loved ones talk with your care team, not medical advice. Read our disclaimer.

The quick guide

What it means: The cancer cells make too much of the HER2 protein, which pushes them to grow. Some are also hormone receptor-positive (HR+/HER2+, sometimes called 'triple-positive'), and get hormone therapy too.

How it's found: An IHC stain scores HER2 from 0 to 3+. A 3+ is positive; a 2+ is checked with a gene test (ISH/FISH).

How common it is: About 15 to 20% of breast cancers are HER2-positive. HER2-low (IHC 1+, or 2+ without gene amplification) is much more common; Cleveland Clinic notes it covers more than half of breast cancers.

How treatment works

🌱 Early-stage

  • Often chemo with Herceptin and pertuzumab first, before surgery, to shrink the tumor.
  • After surgery, HER2 treatment usually continues to complete about a year. If cancer remains at surgery, the ADC trastuzumab emtansine (Kadcyla) is often used.
  • If HR+ too, hormone therapy is added. Some people also get neratinib afterward.

🔁 Advanced or metastatic

  • HER2 drugs keep working in advanced disease: Herceptin plus pertuzumab and a taxane is a common start, then the ADC Enhertu (trastuzumab deruxtecan).
  • Other options include tucatinib with trastuzumab and capecitabine (helpful for brain spread), neratinib or lapatinib, and Kadcyla.

Approvals depend on stage and prior treatment. Your care team will decide what fits you.

Drug guides

Biomarker tests that matter

Side effects you may notice

❓ Questions you and your loved ones can ask

Back to Breast cancer overview. Other types: Hormone receptor-positive (HR+/HER2-) breast cancer, Triple-negative breast cancer (TNBC), Ductal carcinoma in situ (DCIS, stage 0), Inflammatory breast cancer (IBC).

Written by the Cancer Side Effects Guide team from FDA labels and leading cancer centers. Not medical advice. · Last updated: October 15, 2026 · How we write

Not medical advice. This page is general information to help you talk with your care team. It can't replace advice from your doctor or nurse. If you have a fever of 100.4°F (38°C) or higher during treatment, or any symptom that worries you, call your care team now. In an emergency, call 911.

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